fix(lookupNodeModuleSubpath): handle conditions and nested exports (#210

)

Co-authored-by: Pooya Parsa <pooya@pi0.io>

src/resolve.ts

@@ -206,21 +206,23 @@ function _findSubpath(subpath: string, exports: PackageJson["exports"]) {
     return subpath;
   }
 
-  const flattenedExports = _flattenExports(exports);
-  const [foundPath] =
-    // eslint-disable-next-line @typescript-eslint/no-unused-vars
-    flattenedExports.find(([_, resolved]) => resolved === subpath) || [];
-
-  return foundPath;
+  return _flattenExports(exports).find((p) => p.fsPath === subpath)?.subpath;
 }
 
 function _flattenExports(
   exports: Exclude<PackageJson["exports"], string>,
-  path?: string,
-) {
-  return Object.entries(exports).flatMap(([key, value]) =>
-    typeof value === "string"
-      ? [[path ?? key, value]]
-      : _flattenExports(value, path ?? key),
-  );
+  parentSubpath = "./",
+): { subpath: string; fsPath: string; condition?: string }[] {
+  return Object.entries(exports).flatMap(([key, value]) => {
+    const [subpath, condition] = key.startsWith(".")
+      ? [key.slice(1), undefined]
+      : [undefined, key];
+    const _subPath = joinURL(parentSubpath, subpath);
+    // eslint-disable-next-line unicorn/prefer-ternary
+    if (typeof value === "string") {
+      return [{ subpath: _subPath, fsPath: value, condition }];
+    } else {
+      return _flattenExports(value, _subPath);
+    }
+  });
 }

test/utils.test.ts

@@ -108,26 +108,39 @@ describe("lookupNodeModuleSubpath", () => {
   const r = (p: string) => new URL(p, import.meta.url).toString();
 
   const tests = [
+    // Resolve with exports
     {
-      name: "resolves with exports field",
-      input: r("fixture/package/node_modules/subpaths/lib/subpath.mjs"),
+      name: "resolves with exports field (root)",
+      input: r("fixture/package/node_modules/subpaths/dist/index.mjs"),
+      output: "./",
+    },
+    {
+      name: "resolves with exports field (subpath)",
+      input: r("fixture/package/node_modules/subpaths/dist/subpath.mjs"),
       output: "./subpath",
     },
     {
-      name: "resolves with fallback subpath guess",
+      name: "resolves with exports field (with conditions)",
+      input: r("fixture/package/node_modules/postgres/src/index.js"),
+      output: "./",
+    },
+    // Fallbacks
+    {
+      name: "resolves with fallback (non resolved module)",
       input: r("fixture/package/node_modules/alien/lib/subpath.json5"),
       output: "./lib/subpath.json5",
     },
+    {
+      name: "resolves with fallback subpath guess (non existing file)",
+      input: r("fixture/package/node_modules/subpaths/foo/bar.mjs"),
+      output: "./foo/bar.mjs",
+    },
+    // Invalid
     {
       name: "ignores invalid paths",
       input: r("/foo/bar/lib/subpath.mjs"),
       output: undefined,
     },
-    {
-      name: "resolves main export",
-      input: r("fixture/package/node_modules/subpaths/foo/bar.mjs"),
-      output: "./foo/bar.mjs",
-    },
     {
       name: "resolves main export",
       input: r("fixture/package/node_modules/subpaths/"),